The mention of polonium as a possible poison used in Pushkar's murder has led to speculations of the role of a 'highly-placed' and probably 'foreign' person or agency.

The unnatural nature of Pushkar's death is the reason for registering a murder case.Reuters

Since the Delhi police confirmed on Tuesday that Sunanda Pushkar's death was a murder, speculation over the 'unknown persons' who killed her has heated up.

Rumours and theories have been rife ever since the mysterious death of Congress MP Shashi Tharoor's wife last January in a posh New Delhi hotel, hours after her much-publicised Twitter spat with Pakistani journalist Mehr Tarar.

Foreign Hand Suspected: ISI in the Picture?

Theories of the Pakistani intelligence agency's role in the murder have received a fresh lease after experts pointed to the probable use of Polonium-210, a poison said to be available only within nuclear facilities and usually out of reach of a layman. It is produced as a by-product in nuclear fission reactions, and is said to be tightly regulated at nuclear facilities.

Thus, the mention of polonium as a possible poison used in Pushkar's murder has led to speculations of the role of a 'highly-placed' and probably 'foreign' person or agency.

Given that Pushkar had accused Tarar of being a 'Pakistan ISI agent', the role of the agency comes into the picture, and wild rumours suggested the latter sent ISI spies to eliminate Tharoor's wife.

"This is a Pakistani woman who is an ISI (Inter Services Intelligence) agent, and she is stalking my husband," Pushkar had said before her death.

Polonium is said to be deadlier than cyanide, and has allegedly been used in high-profile murders before, including that of Palestinian leader Yasser Arafat and Russian spy Alexander Litvinenko.

Even though the exact poison that killed Pushkar is yet to be determined, medical experts have said the drug that killed her was no 'ordinary' poison.

"The murderer (if proved) would have planned it (the murder) in a smart way so that it would be tough to identify the exact poison. She couldn't have been killed with any normal poison. There have been several cases in which the exact poison, used to kill somebody, was identified even 10 years after the crime was committed," a doctor who was part of the medical team that examined Sunanda's case told India Today.

'Mafia from foreign countries'- Did Dawood Send Contract Killers?

BJP leader Subramanian Swamy, who had been calling Pushkar's death a murder since the beginning, has now speculated that 'gangsters from foreign countries' were behind the murder.

"I found a conspiracy for silence in this case. The people involved were very powerful people. This is a very big murder. Very big names are involved. Even the hotel has to be investigated. But it is not an ordinary murder of passion. It was a murder involving money, a murder that would've hurt the reputation of people in high-profile places," Swamy said, according to Firstpost.

"This murder was carried out by gangsters from foreign countries. It's a national security issue," he added.

The theory of the mafia's role in Pushkar's death rides on her connection to the Indian Premier League, which has been clouded by links with underworld dons such as Dawood Ibrahim and Chhota Shakeel, who were declared offenders in the spot-fixing scandal.

The focus has also been on three people found with fake passports living in the same Delhi hotel around the period of Pushkar's death, with conspiracies floating that the three were sent by Dawood himself, apparently to silence Pushkar who probably knew about underhand financial deals in the IPL, according to the Malayala Manorama.

The Delhi police are also reportedly investigating a list of passengers from Dubai and Pakistan to Delhi on the day of her death.

Swamy took to Twitter again on Wednesday to make another wild assumption – "The crowd that organised Sunanda murder is also behind the campaign to unseat ICC/BCCI Chm Srinivasan. India is Dubai driven nowadays," he tweeted.

Tharoor Involved in Murder?

"Without Tharoor's involvement, this murder couldn't have taken place," one of Pushkar's relatives has said, adding further fuel to the high-profile murder case.

Tharoor will reportedly be interrogated again after the Delhi police changed Pushkar's death case to a murder, stating that everyone connected with the case will be questioned.

"We had said from the beginning that this was a murder case. We want punishment to be given to the people involved in this murder. We want Tharoor to be interrogated. Without Tharoor's involvement, this murder couldn't have taken place," Ashok Kumar, Pushkar's cousin, said.

Swamy had also tweeted last year that Tharoor allegedly received a phone call from his secretary who informed him that 'Pushkar had been terminated'. Tharoor's secretary is also set to be questioned.

What has added to the speculations over Tharoor's role is the major embarrassment he faced following the Twitter scandal, during which Pushkar had alleged that he was having an affair with Tarar.